Electron discharge device of the plural cavity resonator type



July 1, 1947.

P. L. SPENCER ELECTRON DISCHARGE DEVICE 0F THE PLURAL CAVITY RESONATOR TYPE Filed March 2l, 1945 2 Sheets-Sheet l WMM ' july 1, 1947.

P. l.. SPENCER 2,423,161

ELECTRON DISCHARGE DEVICE OF THE PLURAL CAVITY RESONATOR TYPE Filed March 21, 1945 2 Sheets-Sheet 2 Patented July 1, 1947y ELECTRON DISCHARGE DEVICE OF THE PLURAL CAVITY RESONATOR TYPE Percy L. Spencer, West Newton, Mass., assigner to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware y Application March 21, 1945, Serial No. 583,923

7 Claims.

This invention relates to a magnetron and more particularly to one of the type in which a plurality of cavity resonators jointly contribute to the output of the tube.

In devices of the type to which the invention relates the geometry of the cavities determines the frequency of the output. As the desired frequency of the output increases the size of the cavity as heretofore constructed becomes small, and the power output of the tube decreases correspondingly. It is an object of this invention to provide a magnetron of the type described in which the size of the tube does not decrease proportionately to the increase in the frequencies generated.

In my copending application, Serial No. 581,386, iled March 7, 1945, I have disclosed that a magnetron of the above type, having cavity resonators which are adapted to oscillate with substantially equal intensities in a plurality of diierent modes each having a different frequency, can be constructed to deliver an output frequency which is the average of the frequencies of said plurality of modes. y

It is an object of the present invention to provide a novel construction for generating oscillations in a plurality of different modes and having different frequencies.

The foregoing and other objects and features of the invention will be best understood from the following detailed description of one embodiment thereof, reference being had to the accompanying drawing wherein:

Fig. 1 is a longitudinal section through a magnetron embodying the present invention and taken on the line I-I of Fig. 2; and

Fig. 2 is a transverse section taken on the line 2-2 of Fig. 1.

Referring to the drawing, the magnetron there illustrated comprises a tubular envelope of highly conductive material such as copper. yThe ends of the envelope I are covered by caps 2 and 3, likewise of copper, hermetlcally sealed to the body I, as for example, by soldering. A central annular projection 4 is provided on the interior of body I and a ring 5 of substantially lesser external diameter than the internal diameter 'of the projection 4 is supported by a plurality of spacing arms 6 which extend into longitudinal grooves cut in the projection 4. The spacing and supporting arms 6 may be soldered orotherwise integrally connected to the projecting portion 4. A plurality of pairs of short anode arms 8 and 9 are supported in slots extending longitudinally of the interior surface of the ring 5, being securely held in said slots by welding or soldering.

A plurality of pairs of long anode arms I0 and II are supported in longitudinal slots in the interior surface of the annular projection 4. The anode arms 8, 9, I0, and Ilmay be stamped from sheet copper and secured in the supporting grooves by brazing or soldering. Each of the long anode arms I0 and II has a cutout portion I2 of suiicient depth to permit the ring 5 to pass freely therethrough without contact therewith. The inner ends oi both the long arms I0 and II vand the short arms 8 and 9 terminate at the same distance from the center of the tubular body portion l. As illustrated the anode arms are arranged in regularly spaced pairs wih a pair of long arms Ill and II intervening between successive pairs of short arms 8 and 9. The edges of the anode arms B-II facing the center of the tube form electron receiving anode faces which coact with a cathode I3 supported in the center of the body portion I. The cathode I3 has an outer cylindrical surface spaced from and extending parallel with the inner end faces of the anode arms 8--II. The cathode I3 is preferably indirectly heated and the surface thereof coextensive with the anode arms is coated with an electron emissve material. The heating coil may be disposed on the interior of the hollow cylindrical body portion, having its opposite ends connected to end conductors I4 and I5. One of the conductors I4 or I5 is connected to the cylindrical body portion of the cathode to supply a biasing potential thereto and the other of conductors I4 or l5 is insulated therefrom. The cathode is supported and heating and biasing current is supplied thereto by means of lead-in conductors I6 connected to the end conductors I4 and I5 and extending through hollow conducting pipes l1 and glass seals I8 hermetically sealing the outer end of said conducting pipes I 1. The inner ends of conducting pipes II are sealed in openings in the tubular envelope l by soldering or brazing. A pair of magnetic pole pieces I9 provides a magnetic field extending longitudinally through the annular space between the cathode I 3 and the anode arms 8-I I. The magnetic field therefore extends transverse to the path of electron now between the electrode I3 and the end faces of said anode arms. The oscillations generated by the tube may be led offl by way of a coupling loop 20 having one end thereof connected to the end of the connected to a conductor 22 extending axially of the conducting pipe 2i and sealed in a glass seal 23 hermetically closing the outer end of said conducting pipe 2|. It will be understood that the conductor 22 may be continued externally of the glass seal 23 as the central conductor of a coaxial line, the other conductor of which may be connected to the pipe 2| or to the body of the envelope i in a manner known in the art.

In the operation of the above-described device each pair of short anode arms 8 and 9, together with the inner surface of the ring 5 which is intercepted thereby, constitute a cavity which is resonant at the same frequency as that of any other cavity defined by another pair of short arms 8 and 9. Each pair of long anode arms I 8 and passes through notches in the intervening said cathode, said arms being of different length I0 and Il together with the inner surface of the v projecting portion 4 intercepted thereby constitute a cavity which is resonant at the same frequency as that of any other cavity defined by another pair of long arms i0 and Il. Due to the difference in the size of the cavities the frequency generated by any cavity dened by the arms 8 and 9 would be much higher than the frequencies generated in any of the larger cavities defined by the arms I0 and Il, Thus if cavities of the type defined by the arms 8 and 9 alone were present in the tube the length of the wave corresponding to the frequencies generated by the cavities would be small, say four centimeters.

However, due to the small size of a tube comprising only cavities of a size suitable for the generation of four centimeter waves the power output of the tube would be low. If only cavities of the size defined by any pair of arms i0 and Ii were present then the length of the wave corresponding to the frequencies of the oscillations generated in these cavities would be much longer, say eight centimeters. 'I'he power output generated by the larger cavities would be correspondingly higher. By providing cavities of both types in the same tube I have found that the output frequencies assume a value which is intermediate between that of the high frequency and low frequency cavities. Thus if the wave length corresponding to the frequencies generated in the small cavities is four centimeters, and the wave length corresponding to the frequencies `generated in the large cavities is eight centimeters, then the output frequency of the tube will correspond to a wave length of six centimeters, assuming equal intensities of the component frequencies.

The invention, therefore, provides a tube which, due to its larger size, in` this instance corresponding to an eight centimeter tube, may be more readily manufactured than a smaller tube capable of generating six-centimeter waves. The power output of the tube is considerably increased over the output of a tube having the same nurnber of anode cavities but in which the frequencies of all cavities correspond to a wave length of six centimeters. tions, strapping means may be provided connecting like arms. In the instance shown a pair of straps and 28 are provided at the upper end of the anode arms and a similar pair of straps 2l and 28 are provided at the lower end of said arms. The strap 25 is connected to each of the anode arms Il and passes through notches cut in the intervening arms 8, 9, and i0. The strap 26 connects each of the anode arms 8 and passes through notches cut in the intervening arms 9, I0, and Il. At the lower end of the anode arms one of the straps 2l or 28 connects all of the arms In order to limit spurious oscillaand symmetrically disposed in pairs, with a pair of short arms intervening between successive pairs of long arms, each of said pairs of short arms defining a cavity resonator resonant at the same frequency as that of each of the other cavity resonators defined by the other pairs of short arms, each of said pairs of long arms defining a cavity resonator resonant at the same frequency as that of each of the other cavity resonators defined by the other pairs of long arms, and at a lower frequency than that of the cavity resonators defined by the short arms, and means coupled to said magnetron for leading out from said magnetron an output frequency intermediate the resonant frequencies of all of said cavity resonators.

2. A magnetron comprising a hollow metallic body enclosing an evacuated space, a cathode within said space, and a plurality of pairs of long anode arms projecting from the interior wall of said body to points equally spaced from the center thereof, supporting means spaced from the interior wall of said body, a plurality of pairs of short anode arms projecting from the interior wall of said supporting means to points spaced from the center of said body by the same distance as said pairs of long anode arms, each of said pairs of long and short arms defining cavity resonators, one of said pairs of short anode arms intervening between successive pairs of long anode arms, and means coupled to said magnetron for leading out from said magnetron an output frequency intermediate the normal frequencies of the cavity resonators defined by said long arms and said short arms.

3. A magnetron comprising a, hollow metallic body enclosing an evacuated space, a cathode positioned centrally within said space, and a plurality of pairs of long anode arms projecting from the interior wall of said body to points adjacent to and equally spaced from said cathode, supporting means spaced from the interior wall of said body, a plurality of pairs of short anode arms projecting from said supporting means to points adjacent to said cathode and spaced therefrom by the same distance as said pairs of long anode arms, each of said pairs of long and short arms defining cavity resonators, one of said pairs of short anode arms intervening betwen successive pairs of long anode arms, and means coupled to said magnetron for leading out from said magnetron an output frequency intermediate the normal frequencies of the cavity resonators dened by said long and said short arms.

4. A magnetron comprising a hollow metallic body enclosing an evacuated space, a cathode within said space. and a plurality of pairs of long anode arms projecting from the interior wall of said body to points equally spaced from the center thereof, a metallic ring having an exterior diameter substantially less than the interior diameter of said body, a plurality of pairs of short anode arms projecting from the interior wall of said ring to points spaced from the center cf said body by the same distance as said pairs of long anode arms, each of said pairs of long and short arms defining cavity resonators, one of said pairs of short anode arms intervening between successive pairs of long anode arms, and means coupled to said magnetron for leading out from said magnetron an output frequency intermediate the normal frequencies of the cavity resonators defined by said long and said short arms.

5. A magnetron comprising a hollow metallic :body enclosing an evacuated space, a cathode positioned centrally within said space, and a plurality of pairs of long anode arms projecting from the interior wall of said body to points adjacent to and equally spaced from said cathode, a metallic ring having an exterior diametersubstantially less than the interior diameter of said body, a plurality of pairs of short anode arms projecting from the interior Wall of said ring to points adjacent t0 said cathode and spaced therefrom by the same distance as said pairs of long anode arms, each of said pairs of long and shortarms defining cavity resonators, one of said pairs of short anode arms intervening between successive pairs of long anode arms, and means coupled to said magnetron for leading out from said magnetron an output frequency intermediate the normal frequencies of the cavity resonators defined by said long and said short arms.

6. A magnetron comprising a tubular envelope enclosing a cathode, an anode structure including a plurality of anode arms having end faces equally spaced from and adapted to coact with said cathode, said arms being of different length and symmetrically disposed in pairs, a pair of short arms dening a cavity resonator resonant at one frequency, a pair of long arms defining a cavity resonator resonant'at a lower frequency than that of the cavity resonator dened by the short arms, and means coupled to said magnetron for leading out from said magnetron an output frequency intermediate the resonant frequencies of all of said cavity resonators.

7. A magnetron comprising a tubular envelope enclosing a cathode, an anode structure including a plurality of anode arms having end faces equally spaced from and adapted to coaet with said cathode, said arms being of different length and symmetrically disposed in pairs, each pair of short arms dening a cavity resonator resonant at the same frequency as that of each of the other cavity resonators dened by the other pairs of short arms, each pair of long arms dening a cavity resonator resonant at the same frequency as that of each of the other cavity resonators dened .by the other pairs of long arms, and at a lower frequency than that of the cavity reso- REFERENCES CITED rThe following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,400,743 Cliiord May 21, 1946, 2,247,077 BleWett June 24, 1941 2,394,396 Mouromtseff et al. Feb. 5, 1946 

